To investigate the mechanisms involved in PCa (prostate cancer) metastasis and CXCR4 (CXC chemokine receptor-4)-mediated VEGF (vascular endothelial growth factor) and MMP-9 (matrix metalloproteinase-9) expression, we used lentivirus-mediated RNAi (RNA interference) to reduce the expression of CXCR4 in a PCa cell line. We found that the silencing of CXCR4 led to a significant down-regulation of VEGF and MMP-9 at both the mRNA and protein levels compared with the control in vitro. Using an animal model, we confirmed that CXCR4 silencing via subcutaneous injection could reduce tumour growth as well as inhibit metastasis, particularly bone metastasis, of PCa. Using in vivo immunohistochemistry, we also found that the expression of VEGF and MMP-9 were reduced by the knockdown of CXCR4 in the primary tumours of mice. Collectively, our results indicate that CXCR4 plays an important role in PCa metastasis through the up-regulation of VEGF and MMP-9. These findings may aid future intervention strategies.